1. Field of the Invention
The present invention relates to a multilayer ceramic capacitor.
2. Description of the Related Art
In recent years, in order for multilayer ceramic capacitor to miniaturize, obtain larger capacitance, reduce cost and obtain higher reliability, dielectric layers and internal electrode layers are made thinner.
Conventionally, it is known that dielectric particles are added to internal electrode layer paste forming internal electrode layer in order to restrain breaking by firing, sintering of base metal conductive materials such as Ni, etc. (see Japanese Patent Publication (A) No. 5-62855, Japanese Patent Publication (A) No. 2000-277369, Japanese Patent Publication (A) No. 2001-307939, Japanese Patent Publication (A) No. 2003-77761 and Japanese Patent Publication (A) No. 2003-100544). With the tendency of layers being thinner, the dielectric particles, together with Ni particles, are required to be fine.
However, when dielectric particles added to the internal electrode paste are made fine, particle growth of the dielectric particles is accelerated around the phase boundary of dielectric when firing. As dielectric layers are made thinner, throughout the dielectric layers, the ratio of dielectric particles located at a side contacting internal electrode layers become larger and that the particle growth of dielectric particles will have great influence. Consequently, there may be deteriorations in all kinds of characteristics of obtained multilayer ceramic capacitor such as tan δ, bias characteristic, temperature characteristic, reliability, etc.
As a solution to these problems, Japanese Patent Publication (A) No. 2003-124049 discloses techniques to control composition of additives to internal electrode layer paste and to control ratio of average particle sizes of dielectric particles contacting internal electrode layers and dielectric particles not contacting the internal electrode layers after firing, concentration ratio of components of additives, and core-shell ratio. According to said Japanese Patent Publication (A) No. 2003-124049, dielectric layers are possible to be thinner without deteriorating temperature characteristic, tan δ, and lifetime.
However, with the technique as in Japanese Patent Publication (A) No. 2003-124049, an improvement in bias characteristic was not sufficient and there was still a problem to be solved.